We have prepared tungsten bispyrrolyl (Pyr) or bis-2,5-dimethylpyrrolyl (Me 2 Pyr) complexes W(NAr)-(CHCMe 2 Ph)(η 1 -Pyr) 2 (DME) (1), W(NAr)(CHCMe 2 Ph)(η 1 -Me 2 Pyr)(η 5 -Me 2 Pyr) (2), W(NAr Cl )(CHCMe 3 )-(η 1 -Pyr) 2 (DME) (3b), and W(NAr Cl )(CHCMe 3 )(η 1 -Me 2 Pyr)(η 5 -Me 2 Pyr) (4) (Ar ) 2,6-diisopropylphenyl, Ar Cl ) 2,6-dichlorophenyl) in excellent yields by treating the appropriate W(NR)(CHCMe 2 R′)(OTf) 2 -(DME) species with LiPyr or LiMe 2 Pyr. Compounds 2 and 4 react with ethylene slowly to yield stable methylene complexes, W(NAr)(CH 2 )(η 1 -Me 2 Pyr)(η 5 -Me 2 Pyr) (5) and W(NAr Cl )(CH 2 )(η 1 -Me 2 Pyr)(η 5 -Me 2 Pyr) (6). In contrast, treatment of what is believed to be a fortuitous 1:1 mixture of 3b and [W(NAr Cl )(CHCMe 3 )(η 1 -Pyr) 2 ][W(NAr Cl )(CHCMe 3 )(η 1 -Pyr)(η 5 -Pyr)] with ethylene leads to formation of [W(µ-NAr Cl )(η 1 -Pyr) 2 ] 2 (7) in moderate (54%) yield. Compounds 2 and 4 react with [HNMe 2 Ph]-[B(Ar F ) 4 ] (Ar F ) 3,5-(CF 3 ) 2 C 6 H 3 ) in dichloromethane to yield cationic species that contain one η 5 -Me 2 -Pyr ligand and one 2,5-dimethylpyrrolenine ligand formed through addition of a proton to C(2) of a dimethylpyrrolyl ligand, e.g., [W(NAr Cl )(CHCMe 3 )(Me 2 Pyr){NC 4 (H 3 -2,3,4)(Me 2 -2,5)}] + [B(Ar F ) 4 ] -(9). X-ray studies were carried out on 1, 2, 6, 7, and 9.
The bis(benzene-o-dithiol) ligands H(4)-1, H(4)-2, and H(4)-3 react with [Ti(OC(2)H(5))(4)] to give dinuclear triple-stranded helicates [Ti(2)L(3)](4)(-) (L = 1(4)(-), 2(4)(-), 3(4)(-)). NMR spectroscopic investigations revealed that the complex anions possess C(3) symmetry in solution. A crystal structure analysis for (PNP)(4)[Ti(2)(2)(3)] ((PNP)(4)[14]) confirmed the C(3) symmetry for the complex anion in the solid state. The complex anion in Li(PNP)(3)[Ti(2)(1)(3)] (Li(PNP)(3)[13]) does not exhibit C(3) symmetry in the solid state due to the formation of polymeric chains of lithium bridged complex anions. Complexes [13](4)(-) and [14](4)(-) were obtained as racemic mixtures of the Delta,Delta and Lambda,Lambda isomers. In contrast to that, complex (PNP)(4)[Ti(2)(3)(3)] ((PNP)(4)[15]) with the enantiomerically pure chiral ligand 3(4)(-) shows a strong Cotton effect in the CD spectrum, indicating that the chirality of the ligands leads to the formation of chiral metal centers. The o-phenylene diamine bridged bis(benzene-o-dithiol) ligand H(4)-4 reacts with Ti(4+) to give the dinuclear double-stranded complex Li(2)[Ti(2)(4)(2)(mu-OCH(3))(2)] containing two bridging methoxy ligands between the metal centers. The crystal structure analysis and the (1)H NMR spectrum of (Ph(4)As)(2)[Ti(2)(4)(2)(mu-OCH(3))(2)] ((Ph(4)As)(2)[(16]) reveal C(2) symmetry for the anion [Ti(2)(4)(2)(mu-OCH(3))(2)](2)(-). For a comparative study the dicatechol ligand H(4)-5, containing the same o-phenylene diamine bridging group as the bis(benzene-o-dithiol) ligands H(4)-4, was prepared and reacted with [TiO(acac)(2)] to give the dinuclear complex anion [Ti(2)(5)(2)(mu-OCH(3))(2)](2)(-). The molecular structure of (PNP)(2)[Ti(2)(5)(2)(mu-OCH(3))(2)] ((PNP)(2)[17]) contains a complex anion which is similar to [16](2)(-), with the exception that strong N-H...O hydrogen bonds are formed in complex anion [17](2)(-), while N-H...S hydrogen bonds are absent in complex anion [16](2)(-).
Polydentate ligands with benzene-o-dithiolato donor groups are useful building blocks in supramolecular coordination chemistry. The coordination chemistry of bis- and tris(benzene-o-dithiolato) ligands and mixed benzene-o-dithiolato/catecholato ligands is reviewed. These ligands exhibit a versatile coordination chemistry both in solution and in the solid state.
The benzene-o-dithiol/catechol ligands H4-2 and H4-3 react with [TiO(acac)2] to give the dinuclear, double-stranded anionic complexes [Ti2(L)2(mu-OCH3)2](2-) ([22](2-), L=2(4-); [23](2-), L=3(4-)). NMR spectroscopic investigations reveal that the complex anion [Ti2(2)2(mu-OCH3)(2)](2-) is formed as a mixture of three of four possible isomers/pairs of enantiomers, whereas only one isomer of the complex anion [Ti2(3)2(mu-OCH3)(2)](2-) is obtained. The crystal structure analysis of (PNP)2[Ti2(3)2(mu-OCH3)2] shows a parallel orientation of the ligand strands, whereas the structure determination for (AsPh4)2[Ti2(2)2(mu-OCH3)2] does not yield conclusive results about the orientation of the ligand strands due the presence of different isomers in solution, the possible co-crystallisation of different isomers and severe disorder in the crystal. NMR spectroscopy shows that ligand H4-3 reacts at elevated temperature with [TiO(acac)2] to give the triple-stranded helicate (PNP)4[Ti2(3)3] ((PNP)4[24]) as a mixture of two isomers, one with a parallel orientation of the ligand strands and one with an antiparallel orientation. Exclusively the triple-stranded helicates [Ti2(L)(3)](4-) ([25](4-), L=1(4-); [26](2-), L=4(4-)) are formed in the reaction of ligands H4-1 and H4-4 with [TiO(acac)2]. The molecular structures of Na(PNP)3[Ti2(1)3]CH(3)OHH(2)OEt(2)O (Na(PNP)3[25]CH(3)OHH(2)OEt(2)O) and Na(1.5)(PNP)(6.5)[Ti2(4)3]2.3 DMF (Na(1.5)(PNP)(6.5)[26]2.3 DMF) reveal a parallel orientation of the ligand strands in both complexes, which is retained in solution. The sodium cations present in the crystal structures lead to two different kinds of aggregation in the solid state. Na-[25]-Na-[25]-Na polymeric chains are formed from compound Na(PNP)3[25], with the sodium cations coordinated by the carbonyl groups of two ligand strands from two different [Ti2(1)3](4-) ions in addition to solvent molecules. In contrast to this, two [Ti2(4)3](4-) ions are connected by a sodium cation that is coordinated by the three meta oxygen atoms of the catecholato groups of each complex tetraanion to form a central {NaO6} octahedron in the anionic pentanuclear complex {[26]-Na-[26]}(7-).
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